1. Field of the Invention
The present invention relates to a method of controlling a power supply to heat sources of a printer and an apparatus therefor, and more particularly, to a method of controlling the power supply to heat sources of a printer in which the power supply is controlled so that the individual heat sources maintain their desired operating temperatures while periods of power supply to the individual heat sources do not overlap all at once.
2. Description of the Related Art
FIG. 1 is a schematic diagram illustrating a general liquid electrophotographic printer.
Referring to FIG. 1, in a liquid electrophotographic printer, a reset device 15, light scanning devices 16, developing devices 17, a drying unit 18, and a transfer unit 20 are disposed along the circulation path of a photosensitive belt 14 circulated by a plurality of rollers 11, 12 and 13.
In a printing operation, first, the light scanning device 16 scans a light beam along the photosensitive belt 14 circulating past the reset device 15. An electrostatic latent image is formed on the photosensitive belt 14 by the scanning of light. The electrostatic latent image is developed with a developer supplied from the developing device 17. The color image formed on the photosensitive belt 14 is first transferred to a transfer roller 21 as the photosensitive belt 14 continues to advance. Then, the image on the transfer roller 21 is then transferred to a paper 23 when the transfer roller 21 and a fixing roller 22 rotate in contact with each other while causing the paper 23 interposed therebetween to advance.
In the above printer structured so as to perform the above printing operation, there are prerequisite conditions for normal printing operations. In the case of the transfer unit 20, primarily, the surfaces of transfer roller 21 and the fixing roller 22, must be maintained at appropriate preset temperatures. In addition, two heating rollers 18b and 18c must be maintained at a given temperature, since the two heating rollers 18b and 18c periodically evaporate the liquid carrier absorbed in a drying roller 18a while rotating in contact with the drying roller 18a. Here, the drying roller 18a absorbs the liquid carrier remaining on the photosensitive belt 14 while leaving the image forming toner of the liquid developer, supplied from the developing device 17, on the photosensitive belt 14 for developing an electrostatic latent image.
FIG. 2 shows conventional controlling circuits for controlling the power supply to heaters 19b, 19c, 21a and 22a installed in the rollers 18b, 18c, 21 and 22, so that respective heating temperatures required for performing such a printing operation are maintained.
In FIG. 2, the first heater 21a is intended to heat the transfer roller 21, the second heater 22a is intended to heat the fixing roller 22, and the third and fourth heaters 19b and 19c are intended to heat the drying unit 18.
The controlling circuits for controlling the power supply to the individual heaters 19b, 19c, 21a and 22a comprise: switch devices 31, 32, 33 and 34, capable of connecting or disconnecting power from a power supply unit 30 to the respective heaters 19b, 19c, 21a and 22a; thermal sensors 41, 42, 43 and 44 for generating information concerning the temperatures of the respective heat-supplied objects corresponding to the heaters 19b, 19c, 21a and 22a; and, temperature controllers 51, 52, 53 and 54 for controlling the on/off operations of the switch devices 31, 32, 33 and 34 according to the information supplied by the thermal sensors 41, 42, 43 and 44. Such power supply controlling circuits are provided for the respective heaters 19b, 19c, 21a and 22a, independently. Therefore, there may be a time or a period when all the switch devices 31, 32, 33 and 34 are turned on while the temperature controllers 51, 52, 53 and 54 individually control the on/off operations of the switch devices 31, 32, 33 and 34 so as to maintain the set temperatures of the respective heat-supplied objects. When all the switch devices 31, 32, 33 and 34 are turned on, the instantaneous power to be supplied by the power supply unit 30 increases. Consequently, such conventional power supply controlling circuits must be provided with a power supply unit 30 which has a power capacity much larger than that the mean power required for continuous operation. Power supply lines must be compatible with the maximum instantaneous current so as to supply the instantaneous maximum power when all the switch devices 31, 32, 33 and 34 are turned on, and such conventional circuits must satisfy a higher equipment requirement.